@remotion/renderer/dist/get-extra-frames-to-capture.js

Render Remotion videos using Node.js or Bun

"use strict";
// For seamless AAC concatenation, we need to capture a bit of extra audio on both sides
// to later align the audio correctly. This function calculates the exact frames to capture.
Object.defineProperty(exports, "__esModule", { value: true });
exports.getExtraFramesToCapture = void 0;
const combine_audio_1 = require("./combine-audio");
const sample_rate_1 = require("./sample-rate");
// Inspired by https://github.com/wistia/seamless-aac-split-and-stitch-demo
// We can seamlessly concatenate AAC files if we capture a bit of extra audio on both sides in each chunk and then align the audio correctly.
// This function calculates which extra frames should be evaluated for their audio content.
const getExtraFramesToCapture = ({ compositionStart, realFrameRange, fps, forSeamlessAacConcatenation, }) => {
    // If the feature is disabled, don't capture extra frames.
    if (!forSeamlessAacConcatenation) {
        return {
            extraFramesToCaptureAssetsBackend: [],
            extraFramesToCaptureAssetsFrontend: [],
            chunkLengthInSeconds: (realFrameRange[1] - realFrameRange[0] + 1) / fps,
            trimLeftOffset: 0,
            trimRightOffset: 0,
        };
    }
    // If this video is just a chunk as part of a larger video,
    // We also need to know the start time of this chunk to align it correctly.
    const chunkStart = realFrameRange[0];
    // If we are only rendering a portion of the composition, we also need to account for that.
    // It cannot be that the chunk start time is earlier than the composition time.
    if (chunkStart < compositionStart) {
        throw new Error('chunkStart may not be below compositionStart');
    }
    const realLeftEnd = chunkStart - compositionStart;
    if (realLeftEnd < 0) {
        throw new Error('chunkStat - compositionStart may not be below 0');
    }
    const realRightEnd = realLeftEnd + (realFrameRange[1] - realFrameRange[0] + 1);
    // Find the closest AAC packet border and add two AAC packet padding.
    const aacAdjustedLeftEnd = Math.max(0, (0, combine_audio_1.getClosestAlignedTime)(realLeftEnd / fps) - 2 * (1024 / sample_rate_1.DEFAULT_SAMPLE_RATE));
    const aacAdjustedRightEnd = (0, combine_audio_1.getClosestAlignedTime)(realRightEnd / fps) +
        2 * (1024 / sample_rate_1.DEFAULT_SAMPLE_RATE);
    // Now find the additional frames that we need to capture to have enough audio
    const alignedStartFrameWithoutOffset = Math.floor(aacAdjustedLeftEnd * fps);
    const alignedStartFrame = alignedStartFrameWithoutOffset + compositionStart;
    const alignedEndFrame = Math.ceil(aacAdjustedRightEnd * fps) + compositionStart;
    const extraFramesToCaptureAudioOnlyFrontend = new Array(realFrameRange[0] - alignedStartFrame)
        .fill(true)
        .map((_, f) => f + alignedStartFrame);
    const extraFramesToCaptureAudioOnlyBackend = new Array(alignedEndFrame - realFrameRange[1] - 1)
        .fill(true)
        .map((_, f) => f + realFrameRange[1] + 1);
    // But now, we might have too much audio, since the extra frames only have a `1 / fps` step.
    // When creating the lossless audio for a chunk, we need to shave that extra audio off.
    const trimLeftOffset = (aacAdjustedLeftEnd * fps - alignedStartFrameWithoutOffset) / fps;
    const trimRightOffset = (aacAdjustedRightEnd * fps - Math.ceil(aacAdjustedRightEnd * fps)) / fps;
    const chunkLengthInSeconds = aacAdjustedRightEnd - aacAdjustedLeftEnd;
    return {
        extraFramesToCaptureAssetsFrontend: extraFramesToCaptureAudioOnlyFrontend,
        extraFramesToCaptureAssetsBackend: extraFramesToCaptureAudioOnlyBackend,
        chunkLengthInSeconds,
        trimLeftOffset,
        trimRightOffset,
    };
};
exports.getExtraFramesToCapture = getExtraFramesToCapture;